Field of the Invention
This invention relates to a pump for ice-cream machines. More particularly, this invention relates to a pump for feeding an ice-cream liquid mixture from a tank into a whipping cylinder in a machine for the production of soft-type ice-cream.
In this kind of ice-cream machines, the liquid mixture that will become ice-cream is sent from a pasteurizing and temperature-keeping tank to a whipping cylinder, suitable for the product pasteurization as well, where it is stirred, cooled and intimately mixed with air to obtain an ice-cream which in this particular case is of the soft type.
Pumps used for this purpose are generally constituted by gear pumps or rotary pumps.
The major drawbacks of these pumps result from their poor head, the imprecision of their delivery and the poor sealing of the pumping body towards the outside when the pump is not working. All these drawbacks involve a series of inconveniences.
First of all, due to said reduced head, in these pumps the feeding means for air to be mixed with the liquid mixture consist of an open channel which freely connects, i.e. without valves, the pump with ambient air. When the machine is not working or during pasteurization, the air present in the whipping cylinder tends to separate from the mixture and reascends the delivery duct, passing through the pump and the channel and leaving in the cylinder a substantially deaerated mixture, therefore the desired soft-type ice-cream does not form.
Furthermore, when during the pump operation an overpressure occasionally creates in the whipping cylinder and in the delivery duct, the aerated and therefore foamy product comes out from said channel, thus involving obvious inconveniences.
Another inconvenience lies in the fact that when the machine is in the whipping stage without ice-cream delivery, the temperature of the discharge duct and subsequently of the pump gradually falls down to the temperature of the whipping cylinder thus forming crystals which may enter the gears and damage them.
Pumps provided with pistons instead of rotary pumps have been proposed; said pumps, though having better control on head and delivery, however involve, for their configuration and application, inconveniences due to foam formation and/or to the need of being equipped with their own independent motor.